Configure Kubernetes with Kustomize

Kustomize is a Kubernetes configuration transformation tool that lets you customize untemplated YAML files, leaving the original files untouched. Kustomize can also generate resources such as ConfigMaps and Secrets from other representations. Kustomize is built for the Kubernetes API, so it can understand and modify Kubernetes-style objects.

If you want to use Helm charts with Config Sync, there are two supported methods: rendering Helm through Kustomize or using the Helm API. This page details the requirements for rendering Helm charts through Kustomize. For more information about using the Helm API, see Syncing Helm charts from Artifact Registry.

Requirements and limitations

Before setting up automatic rendering with Kustomize, review the following requirements and limitations:

  • Hierarchical sources are not supported.
  • Remote bases from private sources of truth are not supported.
  • Private and OCI-based Helm registries are not supported unless you use the Helm API.
  • Helm values can be managed in the source of truth. With the Helm API, values are managed as part of the RootSync or RepoSync API.
  • Rendering multiple Helm charts in a RootSync or RepoSync object is supported. With the Helm API, you can render only one Helm chart in a RootSync or RepoSync object.
  • Ensure that your Kustomization configuration file (kustomization.yaml, kustomization.yml, or Kustomization) is located in the root of your directory and that all your configurations are stored in that file, not in separate files in your source of truth.

Render Kustomize configurations

The following example demonstrates how you might set up your source of truth to use Kustomize configurations with automatic rendering.

Example architecture for Kustomize configurations

This directory includes four overlays (team-a, team-b, team-c, and external-team) that reference the same base, and a file used by the ConfigMap generator.

The following diagram shows you the directory structure:

├── example
│   ├── base
│   │   ├── kustomization.yaml
│   │   ├── namespace.yaml
│   │   ├── networkpolicy.yaml
│   │   ├── rolebinding.yaml
│   │   └── role.yaml
│   ├── kustomization.yaml
│   ├── README.md
│   ├── team-a
│   │   └── kustomization.yaml
│   ├── team-b
│   │   └── kustomization.yaml
│   └── team-c
│       └── kustomization.yaml
├── external-team
│   └── kustomization.yaml
└── external-data.txt

The following kustomization.yaml file is in the root of the source of truth and it contains references to the four overlays with a ConfigMap generator from a local file:

# ./example/kustomization.yaml
resources:
- team-a
- team-b
- team-c
- ../external-team

configMapGenerator:
- name: my-configmap
  namespace: my-namespace
  files:
    - ../external-data.txt

The following kustomize.yaml is in the team-a directory and is the overlay for team-a:

# ./example/team-a/kustomization.yaml
namespace: team-a

resources:
- ../base

patches:
- target:
   kind: RoleBinding
   name: team-admin-rolebinding
  patch: |-
    - op: replace
      path: /subjects/0/name
      value: team-a-admin@mydomain.com
- target:
   kind: Namespace
   name: default
  patch: |-
    - op: replace
      path: /metadata/name
      value: team-a

The following kustomization.yaml is in the base directory and is the Kustomize base:

# ./example/base/kustomization.yaml
resources:
- namespace.yaml
- rolebinding.yaml
- role.yaml
- networkpolicy.yaml

You can explore an example repository in the configuring namespace-specific policies directory in GitHub.

Render Helm charts through Kustomize

This section explains how to render Helm charts through Kustomize. Bundled Helm and Kustomize versions lists the Kustomize and Helm versions bundled with the corresponding version of Config Sync.

Helm chart fields

You can add the following Helm chart fields to your kustomization.yaml files to support rendering Helm charts through Kustomize:

Field Description
helmGlobals Parameters applied to all Helm charts
helmGlobals.chartHome Accepts a string. A path, relative to the Kustomization root, to a directory containing a subdirectory for each chart to be included in the Kustomization. The default value of this field is charts.
helmGlobals.configHome Accepts a string. Defines a value that Kustomize should pass to Helm with the HELM_CONFIG_HOME environment variable. Kustomize doesn't attempt to read or write this directory. If omitted, TMP_DIR/helm is used, where TMP_DIR is a temporary directory created by Kustomize for Helm.
helmCharts An array of Helm chart parameters
helmCharts.name Accepts a string. The name of the chart. This field is required.
helmCharts.version Accepts a string. The version of the chart
helmCharts.repo Accepts a string. The URL used to locate the chart
helmCharts.releaseName Accepts a string. Replaces RELEASE_NAME in the chart template output
helmCharts.namespace Accepts a string. Sets the target namespace for a release (.Release.Namespace in the template)
helmCharts.valuesInline Values to use instead of default values that accompany the chart
helmCharts.valuesFile Accepts a string. ValuesFile is a local path or a remote URL to a values file to use instead of the default values that accompanied the chart. The default values are in CHART_HOME/NAME/values.yaml.
helmCharts.valuesMerge Accepts merge, override, (default), or replace. ValuesMerge specifies how to treat ValuesInline with respect to Values.
helmCharts.includeCRDs Accepts true or false. Specifies if Helm should also generate CustomResourceDefinitions. The default value is false.

Render a remote Helm chart

Config Sync supports rendering remote Helm charts on clusters that have public internet access.

The following kustomization.yaml renders a remote cert-manager by setting the following helmCharts fields:

# ./kustomization.yaml
...
helmCharts:
- name: cert-manager
  repo: https://charts.jetstack.io
  version: v1.5.3
  releaseName: my-cert-manager
  namespace: cert-manager
...

Render a local Helm chart

Config Sync supports rendering local Helm charts. To use a customized version of a Helm chart, you can pull the released version from the Helm chart (for example, ArtifactHub), make changes locally, and then push the changes to your source of truth.

The following diagram shows you the directory structure:

├── base
│   ├── charts
│   │   └── cert-manager
│   └── kustomization.yaml
├── overlays
│   └── stage
│       └── kustomization.yaml
└── base_value_overrides.yaml

The following kustomization.yaml renders a local cert-manager chart. The default directory for Helm charts is charts and since this chart is checked into the charts directory, you don't need to specify .helmCharts.repo or .helmCharts.version.

# ./overlays/stage/kustomization.yaml
...
# This field is optional if your Helm charts are located in the default 'charts' directory.
helmGlobals:
  chartHome: ../../base/charts
helmCharts:
- name: cert-manager
  releaseName: my-cert-manager
  namespace: cert-manager
  # Specify a local path or a remote URL to a values file instead of using the default values in CHART_HOME/NAME/values.yaml.
  valuesFile: ../../base_value_overrides.yaml
...

Render multiple Helm charts

Config Sync supports rendering multiple Helm charts in one kustomization.yaml file, regardless of whether the chart is remote or local.

The following kustomization.yaml renders a local Helm chart (cert-manager):

# ./kustomization.yaml
...
helmCharts:
- name: cert-manager
  releaseName: my-cert-manager
  namespace: cert-manager
- name: prometheus
  repo: https://prometheus-community.github.io/helm-charts
  version: 14.3.0
  releaseName: my-prometheus
  namespace: monitoring
...

What's next